[FFmpeg-user] Question about mp3 bit rate mode

[桃源老師]

In Addition...

> 2017/01/30 11:54 A.M. 桃源老師 <xanadu6291<at>dream.jp> wrote:
> 
> Hello ffmpeg experts...
> 
> I have question about mp3 bit rate mode.  
> 
> When I run the following command, the resulting duration.mp3 is VBR.  I have confirmed it's bit rate mode with mediainfo, mpg123, and SinkuSuperLite (on Windows).
> 
> $ ffmpeg -f lavfi -i sine=d=300 duration.mp3
> ffmpeg version N-83152-gf7e9275 Copyright (c) 2000-2017 the FFmpeg developers
>  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
>  configuration: --prefix=/Volumes/ffmpeg_compile --pkg-config-flags=--static --disable-ffserver --enable-gpl --enable-version3 --enable-nonfree --enable-libmp3lame --enable-libfdk-aac --enable-libvo-amrwbenc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvorbis --enable-libspeex --enable-libopus --enable-libgsm --enable-libtwolame --enable-libsoxr --enable-libwavpack --enable-libmodplug --enable-libopenjpeg --enable-libwebp --enable-libtheora --enable-libx264 --enable-libopenh264 --enable-libx265 --enable-libxvid --enable-libvpx --enable-libxavs --enable-libfreetype --enable-fontconfig --enable-libfribidi --enable-libass --enable-libbluray --enable-libvidstab --enable-libschroedinger --enable-libsnappy --enable-libzmq
>  libavutil      55. 43.100 / 55. 43.100
>  libavcodec     57. 74.100 / 57. 74.100
>  libavformat    57. 62.100 / 57. 62.100
>  libavdevice    57.  2.100 / 57.  2.100
>  libavfilter     6. 69.100 /  6. 69.100
>  libswscale      4.  3.101 /  4.  3.101
>  libswresample   2.  4.100 /  2.  4.100
>  libpostproc    54.  2.100 / 54.  2.100
> Input #0, lavfi, from 'sine=d=300':
>  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
>    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
> Output #0, mp3, to 'duration.mp3':
>  Metadata:
>    TSSE            : Lavf57.62.100
>    Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, mono, s16p
>    Metadata:
>      encoder         : Lavc57.74.100 libmp3lame
> Stream mapping:
>  Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
> Press [q] to stop, [?] for help
> size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 128x    
> video:0kB audio:2344kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.009457%
> 
> And when I run the following command, the resulting duration.mp3 is CBR.  Confirmed with same program as above.
> 
> $ ffmpeg -f lavfi -i sine=d=300 -write_xing 0 duration.mp3
> ffmpeg version N-83152-gf7e9275 Copyright (c) 2000-2017 the FFmpeg developers
>  built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
>  configuration: --prefix=/Volumes/ffmpeg_compile --pkg-config-flags=--static --disable-ffserver --enable-gpl --enable-version3 --enable-nonfree --enable-libmp3lame --enable-libfdk-aac --enable-libvo-amrwbenc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libvorbis --enable-libspeex --enable-libopus --enable-libgsm --enable-libtwolame --enable-libsoxr --enable-libwavpack --enable-libmodplug --enable-libopenjpeg --enable-libwebp --enable-libtheora --enable-libx264 --enable-libopenh264 --enable-libx265 --enable-libxvid --enable-libvpx --enable-libxavs --enable-libfreetype --enable-fontconfig --enable-libfribidi --enable-libass --enable-libbluray --enable-libvidstab --enable-libschroedinger --enable-libsnappy --enable-libzmq
>  libavutil      55. 43.100 / 55. 43.100
>  libavcodec     57. 74.100 / 57. 74.100
>  libavformat    57. 62.100 / 57. 62.100
>  libavdevice    57.  2.100 / 57.  2.100
>  libavfilter     6. 69.100 /  6. 69.100
>  libswscale      4.  3.101 /  4.  3.101
>  libswresample   2.  4.100 /  2.  4.100
>  libpostproc    54.  2.100 / 54.  2.100
> Input #0, lavfi, from 'sine=d=300':
>  Duration: N/A, start: 0.000000, bitrate: 705 kb/s
>    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
> File 'duration.mp3' already exists. Overwrite ? [y/N] y
> Output #0, mp3, to 'duration.mp3':
>  Metadata:
>    TSSE            : Lavf57.62.100
>    Stream #0:0: Audio: mp3 (libmp3lame), 44100 Hz, mono, s16p
>    Metadata:
>      encoder         : Lavc57.74.100 libmp3lame
> Stream mapping:
>  Stream #0:0 -> #0:0 (pcm_s16le (native) -> mp3 (libmp3lame))
> Press [q] to stop, [?] for help
> size=    2344kB time=00:05:00.01 bitrate=  64.0kbits/s speed= 134x    
> video:0kB audio:2344kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.001875%

The command which produces VBR mp3 file, "$ ffmpeg -f lavfi -i sine=d=300 duration.mp3"'s duration is 5:43 on Mac and is 5:01 on Windows.

The command which produces CBR mp3 file, "$ ffmpeg -f lavfi -i sine=d=300 -write_xing 0 duration.mp3"'s duration is 5:00 on Mac/Win.

So the issue of wrong duration is not only on Mac but also on Win, I think...


Best Regards,


Miya aka Tougen-Roushi
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